The present invention relates to differential mechanisms, and more particularly, to such mechanisms of the type which are controlled by clutch assemblies in which the engagement of the clutch is controlled by an external pressure or vacuum signal.
As used above, the term "differential" merely refers to any device having an input and an output, wherein it is desirable to be able to control the relative rotation (or relative engagement) between the input and the output. However, the invention is especially suited for use with vehicle differentials of the bevel gear or planetary type, and will be described in connection therewith.
A vehicle differential in which the relative rotation between an input and one or more outputs is controlled by a clutch assembly is typically also referred to as a limited slip differential. Limited slip differentials are commonly used in both front and rear drive axle applications, to control or limit the slip between the input and the opposite axle shafts (outputs). However, limited slip differentials may also be used in inter-axle applications, as well as various other applications, and the present invention is not limited to any particular differential configuration or application. Clutch assemblies of the type used to control the relative rotation or slip in limited slip differentials may have the extent of their engagement controlled by some physical phenomenon such as the gear reaction forces within the differential gearing. However, there is a growing interest in being able to control such clutch assemblies in response to an external pressure signal (perhaps ultimately controlled by the vehicle microprocessor), and such clutches are typically referred to as "smart clutches".
One of the problems associated with the use of smart clutches for vehicle differentials is that full engagement of a typical multi-disc clutch pack may require an axial force of several thousand pounds which, in turn, would require hydraulic pressure of at least several hundred PSI. The use and control of such a pressure in a vehicle differential adds substantially to the cost and complexity of the entire system.